The lighting industry is in the midst of a sea change. Driven by a need to provide light sources that require less energy while providing the same amount of light as conventional devices, the industry has moved from high wattage incandescent lamps to more economical fluorescent lamps, including compact fluorescent lamps that can be used in a standard incandescent fixture. As technology continues to develop, fixtures using light emitting diodes (LEDs) have also seen some limited acceptance in the market.
LEDs are solid-state semiconductor devices that emit light when current is applied. LEDs can be highly advantageous over incandescent lamps because LEDs can provide a similar amount of light in a much smaller package that uses much less energy. LEDs also tend to have a much longer useful life than either fluorescent or incandescent lamps.
Despite the many advantages of LED lamps, several factors stand in the way of widespread adoption for household and business lighting applications. First, it is difficult to produce white light with LEDs. Traditional LED technologies result in colored light, typically in shades of red, green, or blue. Although technology exists to create white light with LEDs, this technology adds to the expense of production, and also may not reliably produce a shade of white that is pleasing to consumers, or satisfies certain legal or regulatory requirements. Further, LED lamps can have inconsistent color temperature and light output, as compared to conventional incandescent or fluorescent lamps. This leads to a requirement that each LED lamp produced be tested extensively to ensure that its light output meets specifications, including outputting light with the proper color temperature. This can be particularly important with respect to marketing. Lamp manufacturers find it advantageous to indicate the color temperature of the light output from the lamp (conventionally measured in degrees Kelvin), as well as the total light output (measured in lumens), on their packaging. Making such representation on packaging, however, requires a consistent LED product. One way to verify the consistency of color temperature and total light output of LED products is through testing every individual LED product produced.
Conventionally, this testing has been completed using integrating spheres. Conventional integrating spheres, as the name implies, are typically spherical in shape, have an internal surface colored flat white, and incorporating precision optical measuring equipment. Major manufacturers of integrating spheres include: Sphereoptics, Labsphere, Radiant Imaging, and Orboptronix. When a lamp is introduced into an integrating sphere, the sphere measures precisely the chromaticity values of the light output of the lamp from which color temperature is calculated (expressed in degrees Kelvin) and the total light output (expressed in lumens). Accordingly, depending on the results of an integrating sphere test, it can be determined whether the light output of a given LED lamp meets specifications so as to be appropriate for consumers. Integrating spheres, however, are very expensive, often costing many tens of thousands of dollars. For manufacturers operating multiple LED lamp manufacturing lines, the cost of integrating spheres can cause manufacturing costs to become prohibitive. Thus, it is cost prohibitive to test the chromaticity and total light output of every LED lamp manufactured via conventional integrating spheres.